Charge‐Transport Properties of F₆TNAP‐Based Charge‐Transfer Cocrystals

Abstract

The crystal structures of the charge-transfer (CT) cocrystals formed by the π-electron acceptor 1,3,4,5,7,8-hexafluoro-11,11,12,12-tetracyanonaphtho-2,6-quinodimethane (F 6 TNAP) with the planar π-electron-donor molecules triphenylene (TP), benzo[b]benzo[4,5]thieno[2,3-d]thiophene (BTBT), benzo[1,2-b:4,5-b′]dithiophene (BDT), pyrene (PY), anthracene (ANT), and carbazole (CBZ) have been determined using single-crystal X-ray diffraction (SCXRD), along with those of two polymorphs of F 6 TNAP. All six cocrystals exhibit 1:1 donor/acceptor stoichiometry and adopt mixed-stacking motifs. Cocrystals based on BTBT and CBZ π-electron donor molecules exhibit brickwork packing, while the other four CT cocrystals show herringbone-type crystal packing. Infrared spectroscopy, molecular geometries determined by SCXRD, and electronic structure calculations indicate that the extent of ground-state CT in each cocrystal is small. Density functional theory calculations predict large conduction bandwidths and, consequently, low effective masses for electrons for all six CT cocrystals, while the TP-, BDT-, and PYbased cocrystals are also predicted to have large valence bandwidths and low effective masses for holes. Charge-carrier mobility values are obtained from space-charge limited current (SCLC) measurements and field-effect transistor measurements, with values exceeding 1 cm 2 V −1 s −1 being estimated from SCLC measurements for BTBT:F 6 TNAP and CBZ:F 6 TNAP cocrystals. exhibit properties distinct from those of their individual components. In chargetransfer (CT) cocrystals, one component acts as an π-electron donor (D) and another component acts as a π-electron acceptor (A), and both are typically planar molecules in order to facilitate CT interactions in the solid state. Two major types of molecular stacking motifs are found in CT crystals with 1:1 stoichiometry: mixed stacks, in which D and A molecules alternate along the stacking direction, -D-A-D-A, and segregated stacks, in which donor and acceptor molecules form separate stacks, -D-D-D-and -A-A-A. [1][2][3] When free of disorder, metallic conductivities can be obtained along the stacking direction of CT cocrystals that form segregated stacks and that exhibit extents of CT approximately midway (ρ = ca. 0.5) between the completely neutral (ρ = 0) and fully ionic (ρ = 1) limits. [1][2][3][4] On the other hand, CT cocrystals that consist of mixed stacks generally behave as semiconductors or insulators. [3,5] Recently there has been increasing interest in the semiconducting [6][7][8][9][10][11][12][13][14][15][16][17][18] and photoconductive [19][20][21] properties of mixed-stack cocrystals. Large charge-carrier mobility values, µ, have been reported for several examples using space-charge limited current (SCLC) or field-effect transistor (FET) measurements, includingThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Electronic, vibrational, and charge-transport properties of benzothienobenzothiophene–TCNQ co-crystals

“…These results imply that in BTBT-F m TCNQ hole transport along the DA stacks is less effective than along other directions, a feature similar to that we recently found for co-crystals based on the 1,3,4,5,7,8hexafluoro-11,11,12,12-tetracyanonaphtho-2,6-quinodimethane acceptor. 11 Experimentally, based on OFET device measurements, Sato et al 28 have found n-channel charge transport along the mixedstack direction in the BTBT-F m TCNQ (m = 0, 2, 4) single crystals, with the largest mobility of about 0.2 cm 2 V À1 s À1 observed in the case of BTBT-F 4 TCNQ. Tsutsumi et al 25 have also found predominately n-channel charge transport in OFET devices based on diC 8 BTBT-F m TCNQ (m = 0, 2, 4) co-crystals, with the largest electron mobility 0.4 cm 2 V À1 s À1 , measured along the DA stacks in diC 8 BTBT-F 2 TCNQ.…”

“…Over the last two decades, p-conjugated organic materials have attracted considerable attention for potential applications in various optoelectronic devices [1][2][3][4][5] with organic donor-acceptor (DA) co-crystals being considered as promising materials for OFET (organic field-effect transistor) applications. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] In the case of binary molecular systems, the latter consist of a regular arrangement of D and A molecular moieties with a defined stoichiometry. Usually, DA co-crystals display a ground-state charge transfer (CT) configuration (D r+ -A rÀ ) with a partial ionicity.…”

Thin films of electron donor–acceptor complexes: characterisation of mixed-crystalline phases and implications for electrical doping

“…Mixed stack ordered complexes were reported for combinations of F6TCNNQ with triphenyl, pyrene, phenanthracene, naphtho[1,2-b:5,6-b 0 ]dithiophene 47 or for BTBT, anthracene, carbazole, benzo[1,2-b:4,5-b 0 ]dithiophene. 50 On the basis of the presented data we assume that all shown EDA complex structures are referred to ordered complexes with mixed stacks, also called co-crystals. The strong CT absorption for DBTTF and F6TCNNQ co-deposited films might be a reason for the formation of other crystalline structures.…”

“…45,80 The molecular sizes for DIP in the high temperature bulk phase 80 give roughly the same unit cell parameters as the thin film phase. 82,83 The molecular sizes for the acceptors are taken from mixed crystals reported in literature 50,79 and compared to the single crystal data for F6CTNNQ. 41 Whereas DBTTF and the acceptors have quite similar sizes, DIP is larger along the long axis of the molecule.…”

Organic Cocrystals: Recent Advances and Perspectives for Electronic and Magnetic Applications

“…In addition, Yu et al also achieved the ambipolar charge transport in cocrystals by assembling acceptors with donors of different aromatic conjugated backbones. With the aromatic conjugated backbone of donors increased, the energy levels of supramolecular hybrid orbitals in D/A pairs were higher, contributing to the CT interaction ( Zhang X. et al, 2018 ; Dasari et al, 2019 ). They synthesized four cocrystals using PDICNFN (PDICNF, N′-bis(perfluorobutyl)-1,7- dicyanoperylene-3,4:9,10-bis (dicarboximide) as the acceptor and anthracene, pyrene, perylene, and DPTTA as the donors ( Figure 4A ).…”